TY - THES A1 - Müller, Andreas T1 - Towards functional oxide heterostructures T1 - Funktionelle oxidische Heterostrukturen N2 - Oxide heterostructures attract a lot of attention as they display a vast range of physical phenomena like conductivity, magnetism, or even superconductivity. In most cases, these effects are caused by electron correlations and are therefore interesting for studying fundamental physics, but also in view of future applications. This thesis deals with the growth and characterization of several prototypical oxide heterostructures. Fe3O4 is highly ranked as a possible spin electrode in the field of spintronics. A suitable semiconductor for spin injection in combination with Fe3O4 is ZnO due to its oxide character and a sufficiently long spin coherence length. Fe3O4 has been grown successfully on ZnO using pulsed laser deposition and molecular beam epitaxy by choosing the oxygen partial pressure adequately. Here, a pressure variation during growth reduces an FeO-like interface layer. Fe3O4 films grow in an island-like growth mode and are structurally nearly fully relaxed, exhibiting the same lattice constants as the bulk materials. Despite the presence of a slight oxygen off-stoichiometry, indications of the Verwey transition hint at high-quality film properties. The overall magnetization of the films is reduced compared to bulk Fe3O4 and a slow magnetization behavior is observed, most probably due to defects like anti-phase boundaries originating from the initial island growth. LaAlO3/SrTiO3 heterostructures exhibit a conducting interface above a critical film thickness, which is most likely explained by an electronic reconstruction. In the corresponding model, the potential built-up owing to the polar LaAlO3 overlayer is compensated by a charge transfer from the film surface to the interface. The properties of these heterostructures strongly depend on the growth parameters. It is shown for the first time, that it is mainly the total pressure which determines the macroscopic sample properties, while it is the oxygen partial pressure which controls the amount of charge carriers near the interface. Oxygen-vacancy-mediated conductivity is found for too low oxygen pressures. A too high total pressure, however, destroys interface conductivity, most probably due to a change of the growth kinetics. Post-oxidation leads to a metastable state removing the arbitrariness in controlling the electronic interface properties by the oxygen pressure during growth. LaVO3/SrTiO3 heterostructures exhibit similar behavior compared to LaAlO3/SrTiO3 when it comes to a thickness-dependent metal-insulator transition. But in contrast to LaAlO3, LaVO3 is a Mott insulator exhibiting strong electron correlations. Films have been grown by pulsed laser deposition. Layer-by-layer growth and a phase-pure pervoskite lattice structure is observed, indicating good structural quality of the film and the interface. An electron-rich layer is found near the interface on the LaVO3 side for conducting LaVO3/SrTiO3. This could be explained by an electronic reconstruction within the film. The electrostatic doping results in a band-filling-controlled metal-insulator transition without suffering from chemical impurities, which is unavoidable in conventional doping experiments. N2 - Oxidische Heterostrukturen besitzen verschiedenste physikalische Eigenschaften wie Leitfähigkeit, Magnetisums oder sogar Supraleitung. Diese Effekte, die meist von elektronischen Korrelationen verursacht werden, zu verstehen und ihren fundamentalen Ursprung zu erklären, machen diese Materialsysteme ebenso interessant wie ihr zukünftiges Anwendungspotential. Diese Arbeit beschäftigt sich mit verschiedenen prototypischen Schichtsystemen. Fe3O4 könnte zukünftig als Spinelektrode im Bereich der Spintronik dienen. ZnO ist ein Halbleiter, der durch seinen oxidischen Charakter und einer hinreichenden Spinkohärenzlänge gut zur Spininjektion geeignet ist. Das Wachstum von Fe3O4 auf ZnO wurde erfolgreich mittels gepulster Laserdeposition und Molekularstrahlepitaxie durchgeführt. Dabei ist der Sauerstoffpartialdruck entscheidend und eine Variation des Drucks während des Wachstums wirkt der Bildung einer FeO-artigen Grenzschicht entgegen. Die Filme wachsen inselartig und ihre Gitterstruktur ist fast vollständig relaxiert. Trotz einer Sauerstofffehlstöchiometrie wird die hohe Qualität der Filme durch einen Verwey-Phasenübergang bestätigt. Im Vergleich zu Einkristallen ist die Magnetisierung der Filme reduziert. Durch das Inselwachstum verursachte Antiphasengrenzen könnten zu dieser Reduzierung führen. Die leitfähige Grenzschicht, die in LaAlO3/SrTiO3 Heterostrukturen ab einer bestimmten LaAlO3 Filmdicke auftritt, kann höchstwahrscheinlich durch eine elektronische Rekonstruktion erklärt werden. Im entsprechenden Modell wird der Aufbau eines elektrischen Potentials auf Grund der Polarität des LaAlO3 Films durch eine Ladungsumordnung kompensiert. Die Eigenschaften dieser Heterostruktur sind jedoch von den Wachstumsparametern abhängig. Diese Studie zeigt erstmals, dass die makroskopischen Eigenschaften maßgeblich vom Gesamtdruck, die Anzahl der Ladungsträger dagegen stark vom Sauerstoffpartialdruck während des Wachstums abhängen. Leitfähigkeit auf Grund von Sauerstofffehlstellen wurde für sehr kleine Sauerstoffpartialdrücke beobachtet. Ein zu hoher Gesamtdruck hingegen verhindert die Leitfähigkeit der Grenzschicht. Dies ist vermutlich durch eine Änderung der Wachstumskinematik erklärbar. Ein Nachoxidieren der Proben führt überdies zu einem metastabilen Zustand, der die Vergleichbarkeit von Proben verschiedener Arbeitsgruppen gewährleistet. LaVO3/SrTiO3 zeigt ähnliches Verhalten wie LaAlO3/SrTiO3 und Leitfähigkeit tritt ab einer gewissen LaVO3 Schichtdicke auf. Im Gegensatz zu LaAlO3 ist LaVO3 ein Mottisolator, dass heißt, Korrelationseffekte spielen eine Rolle. LaVO3/SrTiO3 wurde mittels gepulster Laserdeposition hergestellt, Phasenreinheit und die strukturellen Eigenschaften mit verschiedenen Methoden überprüft. Zusätzliche Elektronen wurden für leitfähige Proben auf der LaVO3-Seite der Grenzfläche nachgewiesen. Eine Erklärung hierfür wäre eine elektronische Rekonstruktion im Film selbst. Dieses elektrostatische Dotieren führt zu einem bandfüllungsinduzierten Mott-Phasenübergang, der nicht durch chemische Verunreinigungen, die in konventionellen Dotierexperimenten unvermeidbar sind, beeinflusst ist. KW - Oxide KW - Epitaxieschicht KW - Heterostruktur KW - Physikalische Eigenschaft KW - Heterostrukturen KW - Oxid KW - Wachstum KW - MBE KW - PLD KW - Fe3O4 KW - LaAlO3 KW - LaVO3 KW - heterostructures KW - oxide KW - growth KW - MBE KW - PLD KW - Fe3O4 KW - LaAlO3 KW - LaVO3 KW - Röntgen-Photoelektronenspektroskopie KW - Photoelektronenspektroskopie KW - Kristallwachstum KW - Impulslaserbeschichten KW - Molekularstrahlepitaxie Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-72478 ER - TY - JOUR A1 - García-Martínez, Jorge A1 - Brunk, Michael A1 - Avalos, Javier A1 - Terpitz, Ulrich T1 - The CarO rhodopsin of the fungus Fusarium fujikuroi is a light-driven proton pump that retards spore germination JF - Scientific Reports N2 - Rhodopsins are membrane-embedded photoreceptors found in all major taxonomic kingdoms using retinal as their chromophore. They play well-known functions in different biological systems, but their roles in fungi remain unknown. The filamentous fungus Fusarium fujikuroi contains two putative rhodopsins, CarO and OpsA. The gene carO is light-regulated, and the predicted polypeptide contains all conserved residues required for proton pumping. We aimed to elucidate the expression and cellular location of the fungal rhodopsin CarO, its presumed proton-pumping activity and the possible effect of such function on F. fujikuroi growth. In electrophysiology experiments we confirmed that CarO is a green-light driven proton pump. Visualization of fluorescent CarO-YFP expressed in F. fujikuroi under control of its native promoter revealed higher accumulation in spores (conidia) produced by light-exposed mycelia. Germination analyses of conidia from carO\(^{-}\) mutant and carO\(^{+}\) control strains showed a faster development of light-exposed carO-germlings. In conclusion, CarO is an active proton pump, abundant in light-formed conidia, whose activity slows down early hyphal development under light. Interestingly, CarO-related rhodopsins are typically found in plant-associated fungi, where green light dominates the phyllosphere. Our data provide the first reliable clue on a possible biological role of a fungal rhodopsin. KW - microbial rhodopsins KW - intracellular pH KW - membrane proteins KW - mutants KW - virulence KW - channelrhodopsin-2 KW - growth KW - gene KW - expression KW - bacteriorhodopsin Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149049 VL - 5 IS - 7798 ER - TY - JOUR A1 - Herter, Eva K. A1 - Stauch, Maria A1 - Gallant, Maria A1 - Wolf, Elmar A1 - Raabe, Thomas A1 - Gallant, Peter T1 - snoRNAs are a novel class of biologically relevant Myc targets JF - BMC Biology N2 - Background Myc proteins are essential regulators of animal growth during normal development, and their deregulation is one of the main driving factors of human malignancies. They function as transcription factors that (in vertebrates) control many growth- and proliferation-associated genes, and in some contexts contribute to global gene regulation. Results We combine chromatin immunoprecipitation-sequencing (ChIPseq) and RNAseq approaches in Drosophila tissue culture cells to identify a core set of less than 500 Myc target genes, whose salient function resides in the control of ribosome biogenesis. Among these genes we find the non-coding snoRNA genes as a large novel class of Myc targets. All assayed snoRNAs are affected by Myc, and many of them are subject to direct transcriptional activation by Myc, both in Drosophila and in vertebrates. The loss of snoRNAs impairs growth during normal development, whereas their overexpression increases tumor mass in a model for neuronal tumors. Conclusions This work shows that Myc acts as a master regulator of snoRNP biogenesis. In addition, in combination with recent observations of snoRNA involvement in human cancer, it raises the possibility that Myc’s transforming effects are partially mediated by this class of non-coding transcripts. KW - Drosophila KW - ribosome KW - snoRNA KW - Myc Transcription KW - growth Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-124956 VL - 13 IS - 25 ER - TY - JOUR A1 - Norrmen, Camilla A1 - Figlia, Gianluca A1 - Lebrun-Julien, Frederic A1 - Pereira, Jorge A. A1 - Trötzmüller, Martin A1 - Köfeler, Harald C. A1 - Rantanen, Ville A1 - Wessig, Carsten A1 - van Deijk, Anne-Lieke F. A1 - Smit, August B. A1 - Verheijen, Mark H. G. A1 - Rüegg, Markus A. A1 - Hall, Michael N. A1 - Suter, Ueli T1 - mTORC1 Controls PNS Myelination along the mTORC1-RXR gamma-SREBP-Lipid Biosynthesis Axis in Schwann Cells JF - Cell Reports N2 - Myelin formation during peripheral nervous system (PNS) development, and reformation after injury and in disease, requires multiple intrinsic and extrinsic signals. Akt/mTOR signaling has emerged as a major player involved, but the molecular mechanisms and downstream effectors are virtually unknown. Here, we have used Schwann-cell-specific conditional gene ablation of raptor and rictor, which encode essential components of the mTOR complexes 1 (mTORC1) and 2 (mTORC2), respectively, to demonstrate that mTORC1 controls PNS myelination during development. In this process, mTORC1 regulates lipid biosynthesis via sterol regulatory element-binding proteins (SREBPs). This course of action is mediated by the nuclear receptor RXRg, which transcriptionally regulates SREBP1c downstream of mTORC1. Absence of mTORC1 causes delayed myelination initiation as well as hypomyelination, together with abnormal lipid composition and decreased nerve conduction velocity. Thus, we have identified the mTORC1-RXR gamma-SREBP axis controlling lipid biosynthesis as a major contributor to proper peripheral nerve function. KW - axonal integrity KW - peripheral nervous-system KW - COMPLEX 1 KW - rat hepatocytes KW - SREBP KW - mice KW - growth KW - protein KW - element KW - CNS Myelination Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-114847 SN - 2211-1247 VL - 9 IS - 2 ER - TY - JOUR A1 - Sanz-Moreno, Adrian A1 - Fuhrmann, David A1 - Wolf, Elmar A1 - von Eyss, Björn A1 - Eilers, Martin A1 - Elsässer, Hans-Peter T1 - Miz1 Deficiency in the Mammary Gland Causes a Lactation Defect by Attenuated Stat5 Expression and Phosphorylation JF - PLOS ONE N2 - Miz1 is a zinc finger transcription factor with an N-terminal POZ domain. Complexes with Myc, Bcl-6 or Gfi-1 repress expression of genes like Cdkn2b (p15(Ink4)) or Cd-kn1a (p21(Cip1)). The role of Miz1 in normal mammary gland development has not been addressed so far. Conditional knockout of the Miz1 POZ domain in luminal cells during pregnancy caused a lactation defect with a transient reduction of glandular tissue, reduced proliferation and attenuated differentiation. This was recapitulated in vitro using mouse mammary gland derived HC11 cells. Further analysis revealed decreased Stat5 activity in Miz1 Delta POZ mammary glands and an attenuated expression of Stat5 targets. Gene expression of the Prolactin receptor (PrlR) and ErbB4, both critical for Stat5 phosphorylation (pStat5) or pStat5 nuclear translocation, was decreased in Miz1 Delta POZ females. Microarray, ChIP-Seq and gene set enrichment analysis revealed a down-regulation of Miz1 target genes being involved in vesicular transport processes. Our data suggest that deranged intracellular transport and localization of PrlR and ErbB4 disrupt the Stat5 signalling pathway in mutant glands and cause the observed lactation phenotype. KW - C-MYC KW - transcription factor MIZ-1 KW - breast-cancer cells KW - gene expression KW - epithelial cells KW - prolactin KW - transgenic mice KW - growth KW - differentiation KW - proliferation Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-117286 VL - 9 IS - 2 ER - TY - JOUR A1 - Otto, Wolfgang A1 - Rubenwolf, Peter C. A1 - Burger, Maximilian A1 - Fritsche, Hans-Martin A1 - Rößler, Wolfgang A1 - May, Matthias A1 - Hartmann, Arndt A1 - Hofstädter, Ferdinand A1 - Wieland, Wolf F. A1 - Denzinger, Stefan T1 - Loss of aquaporin 3 protein expression constitutes an independent prognostic factor for progression-free survival: an immunohistochemical study on stage pT1 urothelial bladder cancer JF - BMC Cancer N2 - Background: Treatment of patients with stage pT1 urothelial bladder cancer (UBC) continues to be a challenge due to its unpredictable clinical course. Reliable molecular markers that help to determine appropriate individual treatment are still lacking. Loss of aquaporin (AQP) 3 protein expression has previously been shown in muscle-invasive UBC. The aim of the present study was to investigate the prognostic value of AQP3 protein expression with regard to the prognosis of stage pT1 UBC. Method: AQP 3 protein expression was investigated by immunohistochemistry in specimens of 87 stage T1 UBC patients, who were diagnosed by transurethral resection of the bladder (TURB) and subsequent second resection at a high-volume urological centre between 2002 and 2009. Patients underwent adjuvant instillation therapy with Bacillus Calmette-Guerin (BCG). Loss of AQP3 protein expression was defined as complete absence of the protein within the whole tumour. Expression status was correlated retrospectively with clinicopathological and follow-up data (median: 31 months). Multivariate Cox regression analysis was used to assess the value of AQP3 tumour expression with regard to recurrence-free (RFS), progression-free (PFS) and cancer-specific survival (CSS). RFS, PFS and CSS were calculated by Kaplan-Meier analysis and Log rank test. Results: 59% of patients were shown to exhibit AQP3-positive tumours, whereas 41% of tumours did not express the marker. Loss of AQP3 protein expression was associated with a statistically significantly worse PFS (20% vs. 72%, p=0.020). This finding was confirmed by multivariate Cox regression analysis (HR 7.58, CI 1.29 - 44.68; p=0.025). Conclusions: Loss of AQP3 protein expression in pT1 UBC appears to play a key role in disease progression and is associated with worse PFS. Considering its potential prognostic value, assessment of AQP3 protein expression could be used to help stratify the behavior of patients with pT1 UBC. KW - urothelial bladder carcinoma KW - progression KW - transitional cell carcinoma KW - bacillus calmette guerin KW - water channels KW - follow up KW - in vitro KW - recurrence KW - growth KW - T1 KW - tumor KW - proliferation KW - stage pT1 KW - aquaporin 3 protein KW - immunohistochemistry Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-135679 VL - 12 IS - 459 ER - TY - JOUR A1 - Franke, Katharina A1 - Vilne, Baiba A1 - da Costa, Olivia Prazeres A1 - Rudelius, Martina A1 - Peschel, Christian A1 - Oostendorp, Robert A. J. A1 - Keller, Ulrich T1 - In vivo hematopoietic Myc activation directs a transcriptional signature in endothelial cells within the bone marrow microenvironment JF - Oncotarget N2 - Cancer pathogenesis involves tumor-intrinsic genomic aberrations and tumor-cell extrinsic mechanisms such as failure of immunosurveillance and structural and functional changes in the microenvironment. Using Myc as a model oncogene we established a conditional mouse bone marrow transduction/transplantation model where the conditional activation of the oncoprotein Myc expressed in the hematopoietic system could be assessed for influencing the host microenvironment. Constitutive ectopic expression of Myc resulted in rapid onset of a lethal myeloproliferative disorder with a median survival of 21 days. In contrast, brief 4-day Myc activation by means of the estrogen receptor (ER) agonist tamoxifen did not result in gross changes in the percentage/frequency of hematopoietic lineages or hematopoietic stem/progenitor cell (HSPC) subsets, nor did Myc activation significantly change the composition of the non-hematopoietic microenvironment defined by phenotyping for CD31, ALCAM, and Sca-1 expression. Transcriptome analysis of endothelial CD45-Ter119-cells from tamoxifen-treated MycER bone marrow graft recipients revealed a gene expression signature characterized by specific changes in the Rho subfamily pathway members, in the transcription-translation-machinery and in angiogenesis. In conclusion, intra-hematopoietic Myc activation results in significant transcriptome alterations that can be attributed to oncogene-induced signals from hematopoietic cells towards the microenvironment, e. g. endothelial cells, supporting the idea that even pre-leukemic HSPC highjack components of the niche which then could protect and support the cancer-initiating population. KW - stem-cells KW - mutations KW - C-Myc KW - Rho-GTPases KW - niche KW - leukemia KW - target KW - growth KW - cycle KW - apoptosis, Myc KW - microenvironment KW - endothelial cells Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145844 VL - 6 IS - 26 SP - 21827 EP - 21839 ER - TY - JOUR A1 - Palige, Katja A1 - Linde, Jörg A1 - Martin, Ronny A1 - Böttcher, Bettina A1 - Citiulo, Francesco A1 - Sullivan, Derek J. A1 - Weber, Johann A1 - Staib, Claudia A1 - Rupp, Steffen A1 - Hube, Bernhard A1 - Morschhäuser, Joachim A1 - Staib, Peter T1 - Global Transcriptome Sequencing Identifies Chlamydospore Specific Markers in Candida albicans and Candida dubliniensis JF - PLoS ONE N2 - Candida albicans and Candida dubliniensis are pathogenic fungi that are highly related but differ in virulence and in some phenotypic traits. During in vitro growth on certain nutrient-poor media, C. albicans and C. dubliniensis are the only yeast species which are able to produce chlamydospores, large thick-walled cells of unknown function. Interestingly, only C. dubliniensis forms pseudohyphae with abundant chlamydospores when grown on Staib medium, while C. albicans grows exclusively as a budding yeast. In order to further our understanding of chlamydospore development and assembly, we compared the global transcriptional profile of both species during growth in liquid Staib medium by RNA sequencing. We also included a C. albicans mutant in our study which lacks the morphogenetic transcriptional repressor Nrg1. This strain, which is characterized by its constitutive pseudohyphal growth, specifically produces masses of chlamydospores in Staib medium, similar to C. dubliniensis. This comparative approach identified a set of putatively chlamydospore-related genes. Two of the homologous C. albicans and C. dubliniensis genes (CSP1 and CSP2) which were most strongly upregulated during chlamydospore development were analysed in more detail. By use of the green fluorescent protein as a reporter, the encoded putative cell wall related proteins were found to exclusively localize to C. albicans and C. dubliniensis chlamydospores. Our findings uncover the first chlamydospore specific markers in Candida species and provide novel insights in the complex morphogenetic development of these important fungal pathogens. KW - NRG1 KW - staib agar KW - gene KW - morphogenesis KW - expression KW - regulator KW - virulence KW - growth KW - UME6 KW - epidemiology Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131007 VL - 8 IS - 4 ER - TY - RPRT A1 - Krause, Theresa A1 - Fischer, Doris T1 - Data as the new driver for growth? European and Chinese perspectives on the new factor of production T1 - Sind Daten der neue Wachstumstreiber? Europäische und chinesische Perspektiven auf den neuen Produktionsfaktor N2 - Amidst an emerging international systemic competition between China and the Western world, China’s sustained high economic growth rates, technological innovations and successful control of the corona pandemic have raised doubts over the West’s systemic capabilities. In this context, data resources and regimes play an increasing role. This research note looks at data as present and future driver of innovation and economic growth in more detail. It compares the Chinese and the European perspective on data as well as their respective (planned) policy measures in order to draw tentative conclusions about their different approaches' implications. T3 - CBE Research Note - 1/2021 KW - China KW - Europa KW - Wirtschaftspolitik KW - drivers of growth KW - China KW - data economics KW - European Union KW - growth KW - economic policy KW - data KW - Europe Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-229794 ER - TY - JOUR A1 - Wehner, Marius A1 - Röhr, Merle Insa Silja A1 - Stepanenko, Vladimir A1 - Würthner, Frank T1 - Control of self-assembly pathways toward conglomerate and racemic supramolecular polymers JF - Nature Communications N2 - Homo- and heterochiral aggregation during crystallization of organic molecules has significance both for fundamental questions related to the origin of life as well as for the separation of homochiral compounds from their racemates in industrial processes. Herein, we analyse these phenomena at the lowest level of hierarchy - that is the self-assembly of a racemic mixture of (R,R)- and (S,S)-PBI into 1D supramolecular polymers. By a combination of UV/vis and NMR spectroscopy as well as atomic force microscopy, we demonstrate that homochiral aggregation of the racemic mixture leads to the formation of two types of supramolecular conglomerates under kinetic control, while under thermodynamic control heterochiral aggregation is preferred, affording a racemic supramolecular polymer. FT-IR spectroscopy and quantum-chemical calculations reveal unique packing arrangements and hydrogen-bonding patterns within these supramolecular polymers. Time-, concentration- and temperature-dependent UV/vis experiments provide further insights into the kinetic and thermodynamic control of the conglomerate and racemic supramolecular polymer formation. Homo- and heterochiral aggregation is a process of interest to prebiotic and chiral separation chemistry. Here, the authors analyze the self-assembly of a racemic mixture into 1D supramolecular polymers and find homochiral aggregation into conglomerates under kinetic control, while under thermodynamic control a racemic polymer is formed. KW - perylene bismide dye KW - nucleation-elongation KW - PI stacking KW - polymerization KW - complexity KW - mechanism KW - crystals KW - kinetics KW - growth Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230580 VL - 11 ER -